Method and apparatus for transmitting control information in wireless communication system

ABSTRACT

The present invention relates to a method for receiving a downlink control signal in a TDD-based wireless communication system, and to an apparatus therefor. The method comprises receiving a downlink signal via a downlink interval in a specific frame including the downlink interval, a guard interval and an uplink interval. A combination of the downlink interval, the guard interval and the uplink interval is given using configuration information on the specific subframe. When the configuration information is given such that the length of the downlink interval is larger than a specific value, detecting a first type of PDCCH is performed in the specific subframe. When the configuration information is given such that the length of the downlink interval is equal to or smaller than the specific value, detecting the first type of PDCCH is skipped in the specific subframe.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of transmitting/receiving controlinformation in a TDD (Time Division Duplex)-based wireless communicationsystem and apparatus therefor.

BACKGROUND ART

Generally, a wireless communication system is developing to diverselycover a wide range to provide such a communication service as an audiocommunication service, a data communication service and the like. Thewireless communication is a sort of a multiple access system capable ofsupporting communications with multiple users by sharing availablesystem resources (e.g., bandwidth, transmit power, etc.). For example,the multiple access system may include one of CDMA (code divisionmultiple access) system, FDMA (frequency division multiple access)system, TDMA (time division multiple access) system, OFDMA (orthogonalfrequency division multiple access) system, SC-FDMA (single carrierfrequency division multiple access) system and the like.

DETAILED DESCRIPTION Technical Objects

One object of the present invention is to provide a method and apparatusfor efficiently transmitting/receiving control information in a wirelesscommunication system. Another object of the present invention is toprovide a channel format, resource allocation, a signal processing, andan apparatus therefor to efficiently transmit/receive the controlinformation. Still another object of the present invention is to providea method and apparatus for efficiently allocating resource totransmit/receive the control information.

Technical objects achieved by the present invention are not limited tothe above-mentioned technical objects. And, other unmentioned technicalobjects can be clearly understood from the following description bythose having ordinary skills in the technical field to which the presentinvention pertains.

Technical Solution

In an aspect of the present invention, disclosed herein is a method ofperforming a procedure for receiving a downlink control signal by a userequipment in a TDD (Time Division Duplex)-based wireless communicationsystem, the method comprising receiving a downlink signal via a downlinkperiod in a specific subframe comprising the downlink period, a guardperiod, and an uplink period. A combination of the downlink period, theguard period, and the uplink period is given by using configurationinformation for the specific subframe, if the configuration informationis given such that a length of the downlink period is greater than aspecific value is provided, a detection process for a PDCCH (physicaldownlink control channel) of a first type is performed in the specificsubframe, if the configuration information is given such that the lengthof the downlink period is equal to or less than the specific value, thedetection process for the PDCCH of the first type is skipped, the PDCCHof the first type indicates a PDCCH configured within a resource regionstarting from an Nth OFDM symbol in a subframe, and N is an integer of 2or more.

In another aspect of the present invention, disclosed herein is acommunication device used for in a TDD (time division duplex)-basedwireless, communication system comprising a radio frequency (RF) unitand a processor. The processor is configured to receive a downlinksignal via a downlink period in a specific subframe comprising thedownlink period, a guard period, and an uplink period, a combination ofthe downlink period, the guard period, and the uplink period is given byusing configuration information for the specific subframe, if theconfiguration information is given such that a length of the downlinkperiod is greater than a specific value, a detection process for a PDCCH(physical downlink control channel) of a first type is performed in thespecific subframe, if the configuration information is given such thatthe length of the downlink period is equal to or less than the specificvalue, the detection process for the PDCCH of the first type is skipped,the PDCCH of the first type indicates a PDCCH configured within aresource region starting from a N^(th) OFDM symbol in a subframe, and Nis integers greater than or equals to 2.

Preferably, an extended CP (cyclic prefix) is configured for a downlinktransmission, and the specific value is 6 OFDM symbols.

Preferably, an extended CP is configured for a downlink transmission,and the length of the downlink period is given by a following tableaccording to the configuration information:

Configuration Length of downlink period information (the number of OFDMsymbol) 0 3 1 8 2 9 3 10 4 3 5 8 6 9 7 5

wherein if the configuration information corresponds to #1, #2, #3, #5or #6, the detection process for the PDCCH of the first type isperformed in the specific subframe, and if the configuration informationcorresponds to #0, #4 or #7, the detection process for the PDCCH of thefirst type is skipped in the specific subframe.

Preferably, a normal CP (cyclic prefix) is configured for a downlinktransmission, and the specific value is 3 OFDM symbols.

Preferably, a normal CP (cyclic prefix) is configured for a downlinktransmission, and the length of the downlink period is given by afollowing table in the according to the configuration information:

Configuration Length of downlink period information (the number of OFDMsymbol) 0 3 1 9 2 10 3 11 4 12 5 3 6 9 7 10 8 11 9 6

wherein if the configuration information corresponds to #1 to #4 or #6to #9, the detection process for the PDCCH of the first type isperformed in the specific subframe, and if the configuration informationcorresponds to #0 or #5, the detection process for the PDCCH of thefirst type is skipped in the specific subframe.

Preferably, if the configuration information is given such that thelength of the downlink period is equal to or less than the specificvalue, the detection process for a PDCCH of a second type is performedin the specific subframe and the PDCCH of the second type indicates aPDCCH configured within a resource region of 0^(th) to N−1^(th) OFDMsymbol in a subframe.

Advantageous Effects

According to the present invention, control information can beefficiently transmitted and received in a wireless communication system.In particular, the present invention may be able to provide a channelformat for efficiently transmitting/receiving the control information,resource allocation, a signal processing method. In more particular, thepresent invention may be able to efficiently allocate resource fortransmitting/receiving the control information.

Effects obtainable from the present invention are not limited to theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram for explaining an example of physical channels usedfor 3GPP LTE system and a general signal transmission method using thesame;

FIG. 2 is a diagram for explaining an example of a structure of a radioframe;

FIG. 3 is a diagram for one example of a resource grid for a downlinkslot;

FIG. 4 is a diagram for a structure of a downlink subframe;

FIG. 5 is a flowchart for explaining an example of PDCCH configuringprocess of a base station;

FIG. 6 is a diagram for explaining an example of PDCCH processingprocess of a user equipment;

FIG. 7 is a diagram for a structure of an uplink subframe;

FIG. 8 is a diagram for explaining an example of a carrier aggregation(CA) communication system;

FIG. 9 is a diagram for explaining an example of a cross-carrierscheduling;

FIG. 10 is a diagram for explaining an example of assigning a PDCCH in adata region of a subframe;

FIG. 11 is a diagram for explaining an example of resource allocationfor an E-PDCCH and a PDSCH receiving process;

FIG. 12 is a diagram for explaining an example of a structure of aspecial subframe in case that a normal CP (cyclic prefix) is configured;

FIG. 13 to FIG. 15 indicates an example of PDCCH transmission anddetection according to embodiment of the present invention;

FIG. 16 is a diagram for explaining an example of a base station and auser equipment applicable to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description of embodiments of the present invention mayapply to various wireless access systems including CDMA (code divisionmultiple access), FDMA (frequency division multiple access), TDMA (timedivision multiple access), OFDMA (orthogonal frequency division multipleaccess), SC-FDMA (single carrier frequency division multiple access) andthe like. CDMA can be implemented with such a radio technology as UTRA(universal terrestrial radio access), CDMA 2000 and the like. TDMA canbe implemented with such a radio technology as GSM/GPRS/EDGE (GlobalSystem for Mobile communications)/General Packet Radio Service/EnhancedData Rates for GSM Evolution). OFDMA can be implemented with such aradio technology as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, E-UTRA (Evolved UTRA), etc. UTRA is a part of UMTS (UniversalMobile Telecommunications System). 3GPP (3rd Generation PartnershipProject) LTE (long term evolution) is a part of E-UMTS (Evolved UMTS)that uses E-UTRA and LTE-A (LTE-Advanced) is an evolved version of 3GPPLTE. For clarity, the following description mainly concerns 3GPP LTEsystem or 3GPP LTE-A system, by which the technical idea of the presentinvention may be non-limited.

A user equipment receives information from a base station via a downlink(DL) and transmits information to the base station via an uplink (UL) ina wireless communication system. The information transceived by the basestation and the user equipment includes data and various controlinformation and there may exist various physical channels according to akind and usage of the information transceived by the user equipment andthe base station.

FIG. 1 illustrates a diagram for explaining a general method oftransmitting physical channels used for 3GPP LTE system and signals viathe same.

Referring to FIG. 1, if a power of a user equipment is turned on or theuser equipment enters a new cell, the user equipment may perform aninitial cell search for synchronizing with a base station and the like[S101]. To this end, the user equipment may receive a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the base station, may synchronize with the base station,and then may obtain information such as a cell ID and the like.Subsequently, the user equipment may receive a physical broadcastchannel (PBCH) from the base station and then may be able to obtainbroadcast information within the cell. Meanwhile, the user equipment mayreceive a downlink reference signal (DL RS) and may be then able tocheck a downlink channel state.

Having completed the initial cell search, the user equipment may receivea physical downlink control channel (PDCCH) and a physical downlinkshared channel (PDSCH) according to the physical downlink controlchannel (PDCCH) and may be then able to obtain detailed systeminformation [S102].

Then, the user equipment may be able to perform a random accessprocedure to complete the access to the base station [S103 to S106]. Tothis end, the user equipment may transmit a preamble via a physicalrandom access channel (PRACH) [S103] and may be then able to receive aresponse message via PDCCH and a corresponding PDSCH in response to thepreamble [S104]. In case of a contention based random access, it may beable to perform a contention resolution procedure such as a transmission[S105] of an additional physical random access channel and a channelreception [S106] of a physical downlink control channel and acorresponding physical downlink shared channel.

Having performed the above mentioned procedures, the user equipment maybe able to perform a PDCCH/PDSCH reception [S107] and a Physical UplinkShared Channel/Physical Uplink Control Channel (PUSCH/PUCCH)transmission [S108] as a general uplink/downlink signal transmissionprocedure. Control information transmitted to a base station by a userequipment may be commonly named uplink control information (hereinafterabbreviated UCI). The UCI may include Hybrid Automatic Repeat andreQuest Acknowledgement/Negative-ACK (HARQ-ACK/NACK), Scheduling Request(SR), Channel State Information (CSI), and the like. The CSI may includeChannel Quality Indication (CQI), Precoding Matrix Indication (PMI),Rank Indication (RI) information and the like. In LTE system, the UCI isnormally transmitted via PUCCH by periods. Yet, in case that bothcontrol information and traffic data need to be simultaneouslytransmitted, the UCI may be transmitted on PUSCH. Moreover, the UCI maybe non-periodically transmitted in response to a request/indication madeby a network.

FIG. 2 illustrates an example of a radio frame structure. UL/DL(uplink/downlink) data packet transmission is performed by a unit ofsubframe. And, one subframe is defined as a predetermined time intervalincluding a plurality of OFDM symbols. In the 3GPP LTE standard, atype-1 radio frame structure applicable to FDD (Frequency DivisionDuplex) and a type-2 radio frame structure applicable to TDD (TimeDivision Duplex) are supported.

FIG. 2 (a) is a diagram for a structure of a downlink radio frame oftype 1. A DL (downlink) radio frame includes 10 subframes. Each of thesubframes includes 2 slots. And, a time taken to transmit one subframeis defined as a transmission time interval (hereinafter abbreviatedTTI). For instance, one subframe may have a length of 1 ms and one slotmay have a length of 0.5 ms. One slot may include a plurality of OFDMsymbols in the time domain and may include a plurality of resourceblocks (RBs) in the frequency domain. Since 3GPP LTE system uses OFDM indownlink, OFDM symbol represents one symbol period. The OFDM symbol maybe named SC-FDMA symbol or symbol period. Resource block (RB) is aresource allocation unit and may include a plurality of contiguoussubcarriers in one slot.

The number of OFDM symbols included in one slot may vary in accordancewith a configuration of cyclic prefix (CP). The CP may be categorizedinto an extended CP and a normal CP. For instance, in case that OFDMsymbols are configured by the normal CP, the number of OFDM symbolsincluded in one slot may be 7. In case that OFDM symbols are configuredby the extended CP, since the length of one OFDM symbol increases, thenumber of OFDM symbols included in one slot may be smaller than that ofthe case of the normal CP. In case of the extended CP, for instance, thenumber of OFDM symbols included in one slot may be 6. If a channelstatus is unstable (e.g., a UE is moving at high speed), it may be ableto use the extended CP to further reduce the inter-symbol interference.

When a normal CP is used, since one slot includes 7 OFDM symbols, onesubframe includes 14 OFDM symbols. In this case, first maximum 3 OFDMsymbols of each subframe may be allocated to PDCCH (physical downlinkcontrol channel), while the rest of the OFDM symbols are allocated toPDSCH (physical downlink shared channel).

FIG. 2 (b) is a diagram for a structure of a downlink radio frame oftype 2. A type-2 radio frame includes 2 half frames. Each of the halfframe includes 4 (5) normal subframes and 1 (0) special subframe. Thenormal subframe may be used for UL or DL according to an uplink-downlinkconfiguration. Each of subframes includes 2 slots.

Table 1 is an example of a subframe configuration in a radio frameaccording to the UL-DL configuration.

TABLE 1 Uplink- Downlink- downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D DD D D 6 5 ms D S U U U D S U U D

In Table 1, D indicates a DL subframe, U indicates an UL subframe, and Sindicates a special subframe, respectively. The special subframeincludes DwPTS (downlink pilot time slot), GP (guard period) and UpPTS(uplink pilot time slot). The DwPTS is used for initial cell search,synchronization or channel estimation in a user equipment. The UpPTS isused for channel estimation in a base station and uplink transmissionsynchronization of a user equipment. The guard period is a period foreliminating interference between uplink and downlink, which is generatedin uplink due to multi-path delay of a downlink signal.

The above-described structures of the radio frame are exemplary only.And, the number of subframes included in a radio frame, the number ofslots included in the subframe and the number of symbols included in theslot may be modified in various ways.

FIG. 3 illustrates an exemplary resource grid for a downlink slot.

Referring to FIG. 3, one downlink (DL) slot may include a plurality ofOFDM symbols in the time domain. In particular, one DL slot exemplarilyincludes 7 OFDM symbols and one resource block (RB) exemplarily includes12 subcarriers in the frequency domain, but the present invention is notlimited thereto. Each element on a resource grid is referred to as aresource element (hereinafter abbreviated RE). One resource blockincludes 12×7 resource elements. The number N^(DL) of resource blocksincluded in a DL slot may depend on a DL transmission bandwidth. And,the structure of an uplink (UL) slot may be identical to that of the DLslot.

FIG. 4 illustrates an exemplary structure of a downlink subframe.

Referring to FIG. 4, maximum 3 (4) OFDM symbols situated in a head partof a first slot of one subframe correspond to a control region to whichcontrol channels are allocated. The rest of OFDM symbols correspond to adata region to which PDSCH (physical downlink shared channel) isallocated and a basic resource unit of the data region is an RB.Examples of DL control channels used by LTE may include PCFICH (PhysicalControl Format Indicator Channel), PDCCH (Physical Downlink ControlChannel), PHICH (Physical hybrid automatic repeat request indicatorChannel) and the like. The PCFICH is transmitted in a first OFDM symbolof a subframe and carries information on the number of OFDM symbols usedfor a transmission of a control channel within the subframe. The PHICHis a response to UL transmission and carries a HARQ ACK/NACK (hybridautomatic repeat request acknowledgement/non-acknowledgement) signal.Control information carried on PDCCH may be referred to as downlinkcontrol information (hereinafter abbreviated DCI). The DCI may includeUL scheduling information, DL scheduling information or a UL transmitpower control command for a UE (user equipment) group.

Control information carried on PDCCH may be called downlink controlinformation (DCI: downlink control information). DCI formats of formats0, 3, 3A, and 4 are defined for uplink and DCI formats of formats 1, 1A,1B, 1C, 1D, 2, 2A, 2B, 2C and the like are defined for downlink.According to DCI format, a kind of information field, the number ofinformation field, the number of bits of each information field and thelike may vary. For instance, DCI format may be able to selectivelyinclude a hopping flag, an RB assignment, an MCS (modulation codingscheme), an RV (redundancy version), an NDI (new data indicator), a TPC(transmit power control), a HARQ process number, a PMI (precoding matrixindicator) confirmation and the like according to a usage. Hence, a sizeof control information matched with DCI format may be differentaccording to DCI format. Meanwhile, a DCI format can be used fortransmitting two or more kinds of control information. For instance, DCIformat 0/1A is used for carrying DCI format 0 or DCI format 1, and DCIformat 0 and DCI format 1 are distinguished by a flag field.

PDCCH is able to carry a transmission format for DL-SCH (downlink sharedchannel) and resource allocation, resource allocation information forUL-SCH (uplink shared channel), paging information for PCH (pagingchannel), system information on DL-SCH, resource allocation informationof an upper layer control message such as a random access responsetransmitted on PDSCH, a transmit power control command for individualuser equipments within a random user equipment (UE) group, activation ofVoIP (voice over IP) and the like. A plurality of PDCCHs may betransmitted in a control region and a user equipment may monitor aplurality of PDCCHs. PDCCH is configured with the aggregation of atleast one or more contiguous CCEs (control channel elements). CCE is alogical assignment unit used to provide PDCCH with a code rate inaccordance with a state of a radio channel. CCE corresponds to aplurality of REGs (resource element groups). A format of PDCCH and thenumber of bits of an available PDCCH are determined depending oncorrelation between the number of CCEs and a code rate provided by theCCEs. A base station determines PDCCH format in accordance with DCI tobe transmitted to a user equipment and attaches CRC (cyclic redundancycheck) to the control information. CRC is masked with a uniqueidentifier (called RNTI (radio network temporary identifier)) inaccordance with an owner or usage of PDCCH. If PDCCH is provided for aspecific user equipment, CRC may be masked with a unique identifier ofthe user equipment, i.e., C-RNTI (i.e., Cell-RNTI). As another example,if PDCCH is provided for a paging message, CRC may be masked with apaging indication identifier (e.g., P-RNTI (Paging-RNTI)). If PDCCH isprovided for system information, and more particularly, for a systeminformation block (SIB), which shall be described later, CRC may bemasked with a system information identifier (e.g., SI-RNTI (systeminformation-RNTI). In order to indicate a random access response that isa response to a transmission of a random access preamble of a userequipment, CRC may be masked with RA-RNTI (random access-RNTI).

PDCCH carries a message that is known as DCI (downlink controlinformation) and DCI may include resource allocation information andother control information for one user equipment or UE group. Ingeneral, a plurality of PDCCHs may be transmitted within a subframe.Each PDCCH is transmitted using at least one CCE (control channelelement) and each CCE corresponds to 9 sets of resource elements, eachset comprising 4 resource elements. The 4 resource elements are referredto as an REG (Resource Element Group). 4 QPSK (quadrature phase shiftkeying) symbols are mapped to each REG Resource elements occupied by RS(reference signal) are not included in REG In particular, the totalnumber of REGs in a OFDM symbol may vary depending on whether acell-specific reference signal exists. The concept of REG (i.e., mappingby a unit of group comprising 4 resource elements) may apply to other DLcontrol channels (e.g., PCFICH, PHICH, etc.). In particular, REG is usedfor a basic resource unit of a control region. 4 PDCCH formats aresupported as shown in Table 2.

TABLE 2 PDCCH Number of Number of Number of format CCEs (n) REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

CCEs are numbered contiguously. In order to simplify a decoding process,PDCCH has a format comprising n CCEs and may start in a CCE having anumber corresponding to multiple of n. The number of CCEs used for atransmission of a specific PDCCH is determined by a base station inaccordance with a channel state. For instance, a single CCE may besufficient for a PDCCH provided for a user equipment having a good DLchannel state (e.g., a case that the user equipment is located in thevicinity of a base station). On the other hand, in case of a userequipment having a poor channel state (e.g., a case that the userequipment is located on a cell edge or boundary), 8 CCEs may be requiredfor sufficient robustness. Besides, a power level of PDCCH may beadjusted according to channel condition.

A method introduced to LTE is to define a limited set of CCE positionswhere PDCCH is able to be positioned for each user equipment. Thelimited set of CCE positions for which a user equipment is able tosearch its own PDCCH may be referred to as a search space (SS). In LTEsystem, the search space may have a different size in accordance witheach PDCCH format. And, a UE-specific and common search space areseparately defined. The UE-specific search space may be individuallyconfigured for each user equipment and the range of the common searchspace is known to all user equipments. The UE-specific and common searchspace may be overlapped for a given user equipment. In case that a smallsearch space is given, a base station may be unable to find CCEresources enough to transmit PDCCH to all available user equipments in agiven subframe. In order to minimize this blocking that may be kept in anext subframe, a UE-specific hopping sequence may apply to a start pointof the UE-specific search space.

Table 3 shows sizes of a common search space and a UE-specific searchspace.

TABLE 3 Number of Number of PDCCH Number of PDCCH candidates PDCCHcandidates format CCEs (n) in Common in UE-specific 0 1 — 6 1 2 — 6 2 44 2 3 8 2 2

In order to keep a computation load according to due to the total countof blind decoding (BD) attempts under control, a user equipment is notrequired to perform searches for all the defined DCI formats at the sametime. In general, the user equipment always searches a UE-search spacefor DCI format 0 and DCI format 1A. The DCI format 0 and the DCI format1A are equal to each other in size and may be identified by a flagincluded in a message. And, the user equipment may be required toreceive an additional format, e.g., format 1, 1B, or 2 according to thePDSCH transmission mode configured by a base station. The user equipmentmay be able to search a common search space for DCI format 1A and DCIformat 1C. Moreover, the user equipment may be configured to search forDCI format 3 or DCI format 3A. In this case, the DCI format 3/3A mayhave the same size as that of the DCI format 0/1A, and they may bedistinguished from each other by scrambling CRC with different (common)identifiers other than a UE-specific identifier. PDSCH transmissionscheme according to a transmission mode and information contents of DCIformats are described in following.

Transmission Mode (TM)

-   -   Transmission mode 1: transmission from a single antenna port of        a base station    -   Transmission mode 2: transmit diversity    -   Transmission mode 3: open-loop spatial multiplexing    -   Transmission mode 4: closed-loop spatial multiplexing    -   Transmission mode 5: multi-user MIMO    -   Transmission mode 6: closed-loop rank-1 precoding    -   Transmission mode 7: single antenna port (port 5) transmission    -   Transmission mode 8: double layers transmission (ports 7 and 8)        or single antenna port (port 7 or 8) transmission    -   Transmission mode 9: maximum 8 layers transmission (ports 7        to 14) or single antenna port (port 7 or 8) transmission

DCI format

-   -   Format 0: resource grant for PUSCH transmission (uplink)    -   Format 1: resource assignment for single codeword PDSCH        transmission (transmission modes 1, 2 and 7)    -   Format 1A: compact signaling of resource assignment for single        codeword

PDSCH (all Modes)

-   -   Format 1B: compact resource assignment for PDSCH using rank-1        closed loop precoding (mode 6)    -   Format 1C: very compact resource assignment for PDSCH (e.g.        paging/broadcast system information)    -   Format 1D: compact resource assignment for PDSCH using        multi-user MIMO (mode 5)    -   Format 2: resource assignment for PDSCH for closed-loop MIMO        operation (mode 4)    -   Format 2A: resource assignment for PDSCH for open-loop MIMO        operation (mode 3)    -   Format 3/3A: power control command with 2-bit/1-bit power        adjustment value for PUCCH and PUSCH

In consideration of the above description, a user equipment may berequired to perform maximum 44 times of blind decoding in a singlesubframe. Since checking an identical message with different CRC valuesrequires only a trivial additional computational complexity, checkingthe identical message with different CRC values is not included in countof blind decoding.

FIG. 5 illustrates a flowchart for constructing PDCCH in a base station.

Referring to FIG. 5, a base station generates control informationaccording to a DCI format. The base station may be able to select oneDCI format among a plurality of DCI formats (DCI format 1, 2, . . . , N)according to control information to be transmitted to a user equipment.A CRC (cyclic redundancy check) used for detecting an error is attachedto the control information generated according to each of the DCIformats [S410]. The CRC is masked with an identifier (e.g., RNTI (radionetwork temporary identifier)) in accordance with an owner or usage ofPDCCH. In other words, PDCCH is CRC scrambled with the identifier (e.g.,RNTI).

Table 4 shows an example of identifiers masked to PDCCH.

TABLE 4 Type Identifier Description UE-specific C-RNTI, temporary Usedfor unique identification C-RNTI, semi- of user equipment persistentC-RNTI Common P-RNTI Used for paging message SI-RNTI Used for systeminformation RA-RNTI Used for random access response

In case that a C-RNTI, a temporary C-RNTI, or a semi-persistent C-RNTIis used, PDCCH carries control information for corresponding specificuser equipment. In case that of the other RNTIs are used, PDCCH carriescommon control information which all user equipments within a cellreceive. A base station creates a coded data (codeword) by performing achannel coding on the CRC attached control information [S420]. The basestation performs a rate matching in accordance with a CCE aggregationlevel assigned to a PDCCH format [S430] and generates modulated symbolsby modulating the coded data [S440]. The modulated symbols constructingone PDCCH may have a CCE aggregation level set to one of 1, 2, 4 and 8.Thereafter, the base station maps the modulated symbols to physicalresource elements (REs), i.e., CCE to RE mapping [S450].

FIG. 6 illustrates a flowchart for processing PDCCH in a user equipment.

Referring to FIG. 6, a user equipment de-maps a physical resourceelement to CCE, i.e., RE to CCE demapping [S510]. Since the userequipment does not know which CCE aggregation level should be used toreceive PDCCH, the user equipment performs demodulation with respect toeach of the CCE aggregation levels [S520]. The user equipment performs arate dematching for the demodulated data. Since the user equipment doesnot know which DCI format (or DCI payload size) is used for the controlinformation, the user equipment performs a rate de-matching inaccordance with each DCI format (or DCI payload size) [S530]. The userequipment performs a channel decoding on the rate de-matched dataaccording to a code rate, checks a CRC, and then detects whether thereis an error [S540]. If an error does not occur, it indicates that theuser equipment has found out PDCCH for its own. If an error occurs, theuser equipment continuously performs a blind decoding for a differentCCE aggregation level or a different DCI format (or DCI payload size).The user equipment, which has found out PDCCH of its own, eliminates theCRC from the decoded data and then obtains the control information.

A plurality of PDCCHs for a plurality of user equipments may betransmitted within a control region of an identical subframe. A basestation does not provide the user equipment with information aboutlocation of a corresponding PDCCH within the control region. Hence, theuser equipment searches the subframe for PDCCH for its own in a mannerof monitoring a set of PDCCH candidates. In this case, the term‘monitoring’ means that a user equipment attempts to decode each ofPDCCH candidates in accordance with each of PDCCH formats. This isreferred to as a blind decoding (blind detection). By means of blinddecoding, the user equipment simultaneously performs identification ofPDCCH transmitted to the user equipment and decoding of the controlinformation transmitted on a corresponding PDCCH. For instance, whenPDCCH is de-masked with C-RNTI, if an error does not occur, it indicatesthat the user equipment has found out PDCCH of its own.

Meanwhile, in order to reduce an overhead of blind decoding, the numberof DCI formats is defined less than a kind of the control informationtransmitted on a PDCCH. A DCI format includes a plurality of informationfields different from each other. According to a DCI format, a kind ofthe information field, the number of the information field, a bit numberof each of the information fields and the like may vary. In addition, asize of the control information, which is matched with the DCI format,may vary according to the DCI format. Any DCI format can be used fortransmitting two or more kinds of control information.

FIG. 7 illustrates an exemplary structure of an uplink subframe used inLTE system.

Referring to FIG. 7, an uplink subframe includes a plurality of slots(e.g., 2 slots). A slot may include a different number of SC-FDMAsymbols according to the length of CP. As one example, in case of normalCP, a slot may include 7 SC_FDMA symbols. A UL subframe may be dividedinto a control region and a data region in the frequency domain. Thedata region includes PUSCH and is used for transmitting a data signalsuch as voice and the like. The control region includes PUCCH and isused for transmitting control information. The PUCCH includes a RB pair(e.g., m=0, 1, 2, 3) located at both ends of the data region and hops ona slot boundary. The control information includes HARQ-ACK/NACK, CQI(Channel Quality Information), PMI (Precoding Matrix Indicator), RI(Rank Indication), and the like.

FIG. 8 illustrates an exemplary communication system for carrieraggregation (CA).

Referring to FIG. 8, a wider UL/DL bandwidth can be supported byaggregating a plurality of UL/DL component carriers (CCs). Each of thecomponent carriers may be adjacent to each other or non-adjacent to eachother. The bandwidth of each component carrier may be determinedindependently. An asymmetric carrier aggregation is also possible, whichmeans that the number of downlink component carrier (DL CC) and thenumber of uplink component carrier (UL CC) are different from eachother. Meanwhile, control information may be configured to becommunicated on a specific CC only. The specific CC may be referred toas a primary CC and the other CCs may be referred to as a secondary CC.As one example, in case that a cross-carrier scheduling (or cross-CCscheduling) is applied, PDCCH for DL assignment may be transmitted on aDL CC #0 and corresponding PDSCH may be transmitted on a DL CC #2. Theterm ‘component carrier’ may be replaced by another equivalent term(e.g., a carrier, a cell, and the like).

For cross-CC scheduling, CIF (carrier indicator field) is used. Aconfiguration of whether or not CIF exists within PDCCH may be enabledsemi-statically and user-specifically (or user group-specifically) viaupper layer signaling (e.g., RRC signaling). Basics of PDCCHtransmission may be summarized as follows.

-   -   CIF disabled: PDCCH on DL CC assigns resources for PDSCH on the        same DL CC or resources for PUSCH on a single linked UL CC.        -   No CIF    -   CIF enabled: PDCCH on DL CC assigns resources for PDSCH or PUSCH        to one of multiple aggregated DL/UL CCs using CIF.        -   LTE DCI format expanded to have CIF            -   CIF (when configured) has a fixed x-bit field (e.g.,                x=3)            -   A position of CIF (when configured) is fixed                irrespective of the size of DCI format

In case that a CIF exists within a PDCCH, a base station may assign amonitoring DL CC (set) so that BD complexity is reduced on a userequipment side. For scheduling of PDSCH/PUSCH, a user equipment mayperform detection/decoding of PDCCH on a corresponding DL CC only. Inaddition, the base station may transmit PDCCH via a monitoring DL CConly. A monitoring DL CC set may be configured UE-specifically, UEgroup-specifically or cell-specifically.

FIG. 9 illustrates an exemplary case that 3 DL CCs are aggregated and DLCC A is configured as a monitoring DL CC. If CIF is disabled, each of DLCCs may be able to transmit a PDCCH, which schedules a PDSCH of each ofthe DL CCs, without a CIF according to an LTE PDCCH rule. On the otherhand, if CIF is enabled by upper layer signaling, only DL CC A may beable to transmit a PDCCH, which schedules a PDSCH of a different DL CCas well as a PDSCH of DL CC A using a CIF. PDCCH is not transmitted onDL CC B and DL CC C, which are not configured as a monitoring DL CC. Inthis case, the term ‘monitoring DL CC’ may be replaced by anotherequivalent term such as a monitoring carrier, a monitoring cell, ascheduling carrier, a scheduling cell, a serving carrier, a servingcell, and the like. A DL CC carrying PDSCH corresponding to PDCCH or aUL CC carrying PUSCH corresponding to PDCCH may be referred to as ascheduled carrier, a scheduled cell or the like.

In a 3GPP LTE/LTE-A system, as described with reference to FIG. 4, anFDD DL and TDD DL subframes use first n OFDM symbols of a subframe totransmit PDCCH, PHICH, PCFICH or the like, which is a physical channelused for transmitting various control informations and use the rest ofOFDM symbols to transmit PDSCH. The number of symbols used fortransmitting a control channel in each subframe is delivered to a userequipment dynamically via such a physical channel as PCFICH and the likeor semi-statically via RRC signaling. The n value may be set from 1symbol to maximum 4 symbols according to subframe characteristics andsystem characteristics (FDD/TDD, system bandwidth, etc.). Meanwhile,PDCCH, a physical channel used for transmitting DL/UL scheduling andvarious kinds of control information, is transmitted via a limited OFDMsymbols in a legacy LTE system. Hence, an introduction of an enhancedPDCCH (E-PDCCH), which is multiplexed with PDSCH more freely in a mannerof FDM/TDM, is under consideration.

FIG. 10 illustrates an example of assigning a downlink physical channelto a data region of a subframe.

Referring to FIG. 10, PDCCH according to a conventional LTE/LTE-A system(for convenience, legacy PDCCH) may be assigned to a control region in asubframe (refer to FIG. 4). In the figure, L-PDCCH region means a regionto which legacy PDCCH is able to be assigned. According to the context,a L-PDCCH region may mean a control region, a control channel resourceregion (i.e., CCE resource) where PDCCH is practically assigned, or aPDCCH search space. Meanwhile, PDCCH may be additionally assigned to adata region (e.g., a resource region for PDSCH, refer to FIG. 4). ThePDCCH assigned to a data region is referred to as an E-PDCCH. Althoughthe figure shows a case that one E-PDCCH exists in one slot, this is forexemplary purposes only. The E-PDCCH may exist by a subframe unit (i.e.,through two slots). As shown, by additionally obtaining control channelsresources by means of E-PDCCH, scheduling limitations due to the limitedcontrol channel resources of L-PDCCH region can be alleviated.

In the following description, a method of allocating and managing aresource for a DL control channel by using a data region (e.g., PDSCH)in a subframe is described with reference to drawings. For convenience,although the following description is described centering on therelationship between a base station and a user equipment, the presentinvention may be identically/similarly applied to the relationshipbetween a base station and a relay or the relationship between a relayand a user equipment as well. Hence, the relationship between a basestation and a UE may be replaced by the relationship between a basestation and a relay or the relationship between a relay and a UE in thefollowing description. From the perspective of receiving a signal, arelay and a UE may be generalized as a receiving end. In case that arelay operates as a receiving end, E-PDCCH may be replaced by R-PDCCH(relay-PDCCH).

First, E-PDCCH is explained in more detail. E-PDCCH carries DCI.Regarding DCI, refer to the description with reference to Table 2. Forinstance, E-PDCCH may be able to carry DL/UL scheduling information. Theprocess for E-PDCCH/PDSCH or E-PDCCH/PUSCH is identical/similar to thedescription with reference to S107 and S108 of FIG. 1. That is, a userequipment receives an E-PDCCH and may be then able to receivedata/control information via a PDSCH corresponding to the E-PDCCH. And,the user equipment receives an E-PDCCH and may be then able to transmitdata/control information via a PUSCH corresponding to the E-PDCCH.Processes for E-PDCCH transmission (e.g., channel coding, interleaving,multiplexing, and the like) may be performed using the processes definedfor the conventional LTE (refer to FIGS. 5 and 6) within a varying scopeand may be modified as necessary.

Meanwhile, the conventional LTE system employs that a PDCCH candidateregion (hereinafter, PDCCH search space) is reserved in advance within acontrol region and a PDCCH for a specific user equipment is transmittedvia a part of the reserved region. Hence, a user equipment may be ableto obtain PDCCH of its own in a PDCCH search space via a blind decoding.Similarly, E-PDCCH may be transmitted through a part or a whole ofpre-reserved resources.

FIG. 11 illustrates an exemplary process for resource allocation andreceiving of E-PDCCH.

Referring to FIG. 11, a base station transmits E-PDCCH resourceallocation (RA) information to a user equipment [S1210]. The E-PDCCH RAinformation may include RB (or VRB (virtual resource block)) assignmentinformation. The RB assignment information may be provided by a RB unitor a RBG (resource block group) unit. A RBG includes 2 or morecontiguous RBs. The E-PDCCH RA information may be transmitted using anupper layer (e.g., RRC) signaling. In this case, the E-PDCCH RAinformation is used to pre-reserve an E-PDCCH resource (region). Then,the base station transmits an E-PDCCH to the user equipment [S1220]. TheE-PDCCH may be transmitted within a part or a whole of E-PDCCH resources(e.g., M number of RBs) reserved in the step S1210. Hence, the userequipment monitors a resource (region) (hereinafter an E-PDCCH searchspace, simply a search space) via which the E-PDCCH may be transmitted[S1230]. The E-PDCCH search space may be given as a part of the RB setassigned in the step S1210. In this case, monitoring may include blinddecoding a plurality of E-PDCCH candidates in the search space.

Example Transmission of Control Information in Consideration of aSpecial Subframe

In case of a TDD-based LTE (LTE-A) system, as shown in FIG. 2( b), atiming gap is necessary when a DL subframe converts to a UL subframe. Tothis end, a special subframe (SF) is included between a DL SF and a ULSF. A special SF may have various configurations according to situationssuch as radio conditions, the position of a UE, and the like.

Table 5 shows an example of a special SF. In a special SF,DwPTS/GP/UpPTS may be variously configured according to combinations ofspecial SF configuration (simply, S configuration) and CP.

TABLE 5 Normal cyclic prefix in downlink UpPTS Normal Extended cyclicprefix in downlink cyclic Extended UpPTS Special prefix cyclic NormalExtended subframe in prefix cyclic prefix cyclic prefix configurationDwPTS uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192 ·T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) (3 symbols)(3 symbols) 1 19760 · T_(s) 20480 · T_(s) (9 symbols) (8 symbols) 221952 · T_(s) 23040 · T_(s) (10 symbols) (9 symbols) 3 24144 · T_(s)25600 · T_(s) (11 symbols) (10 symbols) 4 26336 · T_(s)  7680 · T_(s)4384 · T_(s) 5120 · T_(s) (12 symbols) (3 symbols) 5  6592 · T_(s) 4384· T_(s) 5120 · T_(s) 20480 · T_(s) (3 symbols) (8 symbols) 6 19760 ·T_(s) 23040 · T_(s) (9 symbols) (9 symbols) 7 21952 · T_(s) — — — (10symbols) 8 24144 · T_(s) — — — (11 symbols)

In Table 5, a number in bracket indicates the length of a DwPTS periodrepresented by the number of OFDM symbols. For convenience, a DL SF, aUL SF, and a special SF are denoted by D, U, and S, respectively.

FIG. 12 shows the number of OFDM symbols in DwPTS, GP, and UpPTSaccording to configurations of Table 5. For convenience, FIG. 12 showsan exemplary case that normal CP is used (that is, 14 OFDM symbols persubframe). Referring to FIG. 12, the number of OFDM symbols availablefor a DL transmission (i.e., DwPTS) varies according to S configuration.Specifically, in case of S configuration #0 and #5, first 3 OFDM symbolsof the first slot may be used for DwPTS. On the contrary, in case of Sconfiguration #1, #2, #3, #4, #6, #7, #8, all OFDM symbols of the firstslot may be used for DwPTS.

As shown in FIG. 12, in case of a specific S configuration having ashort DwPTS period (e.g., S configuration #0 or #5), a PDSCH region doesnot exist or partly exists in a S SF. Hence, in case that E-PDCCH isemployed in a TDD system, it may not be possible to use E-PDCCH in a SSF according to an S configuration or may be inevitable to use E-PDCCHhaving a structure different from that of a general D. In this case, ageneral D may indicate a subframe configured as D according to the UL-DLconfiguration (e.g., Table 1). In the present specification, D means ageneral D if there is no specific mention.

In the following description, the present invention proposes a method ofconfiguring a PDCCH search space (SS) in a S SF and a method oftransmitting/receiving PDCCH, in case that E-PDCCH is configured to usein a TDD system.

In this case, an L-PDCCH region may mean a control region, a controlchannel resource region (e.g., CCE resource) to which a PDCCH can beassigned within the control region, or a PDCCH search space according tothe context. Similarly, an E-PDCCH region may mean a data region (referto FIG. 4), a control channel resource region to which PDCCH can beassigned within the data region (i.e., a VRB resource allocated by anupper layer; refer to FIG. 11), or an E-PDCCH search space.

In this case, legacy PDCCH and E-PDCCH may be collectively referred toas PDCCH unless they are treated differently.

For convenience, the present invention is explained under the followingassumptions.

-   -   4 kinds of CCE aggregation levels (L=1, 2, 4, 8) exist and the        number of PDCCH candidates for CCE aggregation levels is defined        by 6, 6, 2, and 2, respectively. For convenience, it is assumed        that an E-PDCCH of a aggregation level L is transmitted through        L number of RBs.    -   Maximum 3 kinds of DCI format groups may be configured according        to transmission modes. DCI format group may be defined by        purpose/function/characteristics and the like. For instance, a        DCI format group includes (i) a DL-dedicated DCI format group        used only for DL scheduling (e.g., DCI format 2), (ii) a        DL/UL-common DCI format group used for selectively performing        DL/UL scheduling in a manner of sharing one DCI payload size        (e.g., DCI format 0/1A), (iii) a UL-dedicated DCI format group        used only for UL scheduling (e.g., DCI format 4). A DCI format        group may be replaced by a PDCCH candidate group. A PDCCH        candidate group may be classified according to a CCE aggregation        level (irrespective of a DCI format). In addition, a PDCCH        candidate group may be configured by different subsets for PDCCH        candidates within CCE aggregation levels.

Although the present invention is explained based on a CCE aggregationlevel for coding PDCCH, the number of PDCCH candidates for which blinddecoding should be performed, a DCI format for DL/UL scheduling, and thelike as defined in the conventional LTE/LTE-A system, it is apparentthat the present invention may be expanded/applied to a aggregationlevel, the number of PDCCH candidates, a DCI format and the like, whichwill be added or modified to a future standard in a similar manner.

The present invention is now described in detail. The followingdescription is described centering on E-PDCCH transmission/reception ina special subframe. Hence, a detailed explanation on operations in ageneral D and L-PDCCH may refer to the conventional art.

First, a method of configuring a SS in a general D is described asfollows (Alt 1 to 2).

-   -   Alt 1: assigning a SS to an E-PDCCH region within a 1^(st) slot        and an E-PDCCH region within a 2^(nd) slot        -   DCI formats are classified into DCI format group X or Y. A            SS for DCI format group X may be configured in an E-PDCCH            (PDSCH) region within the 1^(st) slot and the SS for DCI            format group Y may be configured in the E-PDCCH (PDSCH)            region within the 2^(nd) slot. The SS for DCI format X or Y            may be configured with at least 4 OFDM symbols.    -   Alt 2: assigning a SS to an E-PDCCH region within a 1^(st) slot        and an E-PDCCH region within a 2^(nd) slot        -   DCI formats are classified into DCI format group A, B or C.            A SS for DCI format group A may be configured in the            conventional L-PDCCH region, and a SS for DCI format group B            or C may be configured in an E-PDCCH (PDSCH) region within            the 1^(st) slot and the 2^(nd) slot, respectively. The SS            for DCI format B or C may be configured with at least 4 OFDM            symbols.

In case that a SS for PDCCH transmission/detection in a general D isconfigured as mentioned above, a method of transmitting/detecting PDCCHin a S SF and a method of configuring a SS for the same are described asfollows.

-   -   Sol 1: Transmission/detection for a PDCCH that is to be        scheduled via the S SF is performed in a D before the        corresponding S SF. That is, E-PDCCH transmission/reception is        not performed in the S SF.        -   Transmission/detection for PDCCH (S-PDCCH) that is            configured to be scheduled via S SF may be performed in D            which exists (right) before a corresponding S SF, instead.            In this case, distinguishing between S-PDCCH and PDCCH            (D-PDCCH) that is originally configured to be scheduled in D            is performed by 1) independently configuring SS for S-PDCCH            and SS for D-PDCCH (separate signaling may be additionally            accompanied to allocate a SS resource (e.g., CCE or RE) for            S-PDCCH within an E-PDCCH region of D), 2) commonly            configuring SS for S-PDCCH and D-PDCCH and including a flag            (e.g., 1 bit) in corresponding PDCCH, the flag used for            distinguishing between S-PDCCH and D-PDCCH. In this case, SS            structure for S-PDCCH may be configured in a manner            identical to SS structure of a general D.

FIG. 13 illustrates an example of performing transmission/reception ofPDCCH according to Sol 1. It is assumed that UL-DL configuration #1 isconfigured in the present example. Referring to FIG. 13, a PDCCH for a SSF (special subframe) (S-PDCCH) is detected in a D which exists (right)before the S SF, instead ({circle around (1)}). If the S-PDCCH isdetected in the D, the user equipment may receive a PDSCH signal in acorresponding S SF or may transmit a PUSCH signal in a U correspondingto the S SF ({circle around (2)}).

-   -   Sol 2: Transmission/detection for all PDCCHs (DCI formats) is        performed only via an L-PDCCH region in S SF. That is, E-PDCCH        transmission/reception/detection is not performed in S SF.        -   In S SF, transmission/detection for all PDCCHs (DCI formats)            is performed only via an L-PDCCH region. The present method            can be applied irrespective of a PDCCH transmission            structure in a general D and an S configuration (i.e., the            length of DwPTS period). For instance, in case that Alt 1 is            applied to a general D, one SS can be commonly configured in            an L-PDCCH region for DCI group X, Y in a S SF. (thereby,            PDCCH transmission/detection for both DCI format groups X            and Y may be performed). In addition, in case that Alt 2 is            applied to a general D, PDCCH transmission/detection for all            the DCI format groups A, B, and C may be performed via an SS            within a L-PDCCH region configured for DCI format group A in            the S SF.

FIG. 14 illustrates an example of performing PDCCHtransmission/reception according to Sol 2. Referring to FIG. 14, a PDCCHtransmission/detection process in a general D may be performed forL-PDCCH and/or E-PDCCH according to a subframe configuration. On theother hand, a PDCCH detection process may be performed on the assumptionthat E-PDCCH is not transmitted in S SF irrespective of S configuration({circle around (2)}). That is, a PDCCH detection process can beperformed for L-PDCCH only in S SF.

-   -   Sol 3: Differently configuring a PDCCH (DCI format) transmission        region according to S configuration (e.g., the length of DwPTS        period)        -   SS configuration for transmitting/detecting PDCCH (DCI            format) may be configured differently according to S            configuration (e.g., the length of DwPTS period) (e.g.,            Table 5) in S SF. A detailed method is described as follows.

1) Case #1: in case that the number of OFDM symbols within DwPTS is lessthan M (e.g., M=6): Sol 2 may be applied. That is,transmission/detection of all PDCCHs (DCI formats) can be performed onlyvia a L-PDCCH region in S SF. On the other hand, from the perspective ofE-PDCCH, in case that the number of OFDM symbols within DwPTS is lessthan M (e.g., M=6), a user equipment may operate on the assumption thatthere is no E-PDCCH in S SF. That is, a user equipment may not expectreception of E-PDCCH in S SF and thus may not perform an E-PDCCHreceiving process (e.g., E-PDCCH monitoring, blind decoding, and thelike). Instead, as suggested earlier, PDCCH (DCI format) can betransmitted/received/detected via a L-PDCCH region in S SF in whichE-PDCCH monitoring is not performed. Meanwhile, since the number of OFDMsymbols within DwPTS is given by using S configuration as shown in Table5, the present method may be equivalently represented using Sconfiguration. For instance, the present method may be understood as anoperation performed when a specific S configuration(s) is configured. Inthis case, the specific S configuration means a S configuration that thenumber of OFDM symbols within DwPTS is less than M (e.g., M=6).Referring to Table 5, the present method may be applied to Sconfiguration #0 or #5 in case of DL normal CP, and may be applied to Sconfiguration #0 or #4 in case of DL extended CP, but is not limitedthereto.

2) Case #2: in case that the number of OFDM symbols within DwPTS isgreater than N (e.g., N=7) (N>M, (e.g., N=M+1)): transmission/detectionof PDCCH (DCI format) may be performed in an E-PDCCH region in S SF. Ifthe present method is equivalently represented using S configuration,referring to Table 5, the present method may be applied to Sconfiguration #1 to #4 or #6 to #8 in case of DL normal CP, and may beapplied to S configuration #1 to #3 or #5 to #7 in case of DL extendedCP. Meanwhile, in case that Alt 1 is applied to a general D, only anE-PDCCH region can be configured even in S SF. That is, in S SF in whichis permitted to transmit E-PDCCH, a user equipment may perform adetecting process for E-PDCCH (e.g., monitoring E-PDCCH candidates), andmay omit/skip a detecting process for L-PDCCH. On the other hand, incase that Alt 2 is applied to a general D, both a L-PDCCH region and anE-PDCCH region may be configured in S SF. That is, in S SF in which ispermitted to transmit E-PDCCH, a user equipment may perform a detectingprocess for both L-PDCCH and E-PDCCH. From the perspective of blinddecoding complexity, in S SF in which is permitted to transmit E-PDCCH,it is preferable to perform transmission/reception/detection of E-PDCCH.Meanwhile, the size of a E-PDCCH region is limited in S SF due to GP andUpPTS. If E-PDCCH (DCI format)/E-PDCCH SS is defined by a slot unit, thefollowing three methods (Opt 1 to 3) may be considered.

-   -   Opt 1: PDCCH transmitted/detected via an E-PDCCH region within a        second slot in a general D may be configured to be        transmitted/detected via an L-PDCCH region in S SF. For        instance, in case that Alt 1 is applied to a general D, SSs for        DCI format groups X and Y may be configured in an E-PDCCH region        within a first slot and an L-PDCCH region in the S SF,        respectively. In addition, in case that Alt 2 is applied to a        general D, SSs for DCI format groups A and B may be configured        in a L-PDCCH region and an E-PDCCH within a first slot,        respectively. That is, PDCCH transmission/detection of both DCI        format groups A and C may be performed via the SS in a L-PDCCH        region which is configured for DCI format group A.

In case of applying Opt 1, it is advantageous in that an E-PDCCHstructure applied to a general D can be re-used in S SF without anymodification/transformation, since the conventional L-PDCCH is re-used.

-   -   Opt 2: PDCCHs transmitted/detected via E-PDCCH regions within        first and second slots in a general D may be configured to be        transmitted/detected via a L-PDCCH region and an E-PDCCH region        within the first slot in S SF, respectively. For instance, in        case that Alt 1 is applied to a general D, SSs for DCI format        groups X and Y may be configured in a L-PDCCH region and an        E-PDCCH region within the first slot in a S SF, respectively. In        addition, in case that Alt 2 is applied to a general D, SSs for        DCI format groups A and C may be configured in a L-PDCCH region        and a E-PDCCH region within the first slot in S SF,        respectively. That is, PDCCH transmission/detection of both DCI        format groups A and B may be performed via the SS in a L-PDCCH        region which is configured for DCI format group A.

In case of applying Opt 2, a decoding order for each DCI format group ina general D can be maintained identically for S (time axis) as well.Therefore, a stable signal processing in a user equipment can beguaranteed by early decoding of DL data and the like.

-   -   Opt 3: a PDCCH, which is transmitted/detected via an E-PDCCH        region within a first and second slots in a general D, may be        configured to be transmitted/detected only via an E-PDCCH region        within the first slot in a S SF. For instance, in case that Alt        1 is applied to a general D, a SS for a DCI format group X may        be configured in the E-PDCCH region within the first slot in the        S SF. That is, PDCCH transmission/detection for both DCI format        groups A and B may be performed via the corresponding SS. And,        in case that Alt 2 is applied to a general D, the SS for DCI        format groups A and B may be respectively configured in the        L-PDCCH region and the E-PDCCH region within the first slot, in        the S SF. That is, PDCCH transmission/detection for both DCI        format groups B and C may be performed via the SS which is        configured for DCI format group B. As an alternative, in case        that Alt 1 is applied to a general D, the SS for DCI format        groups X and Y may be independently configured in the E-PDCCH        region within the first slot in the S SF. And, in case that Alt        2 is applied to the general D, the SS for the DCI format group A        is configured in the L-PDCCH region and the SS for each of DCI        format group B or C may be independently configured in the        E-PDCCH region within the first slot. In this case, in order to        additionally configure a SS (or a SS for DCI format group C) for        DCI format group Y in the E-PDCCH region within the first slot        of the S SF, signaling may be additionally accompanied to        allocate a SS resource (e.g., CCE or RE).

In case of applying Opt 3, the DCI format group capable of beingtransmitted via the E-PDCCH region in the general D is identicallymaintained in the S SF as well. Therefore, it may be possible totransmit a PDCCH having a strong tolerance to an interference occurringfrom an L-PDCCH region and securing an enhanced performance (via using aUE-specific DMRS and the like).

Meanwhile, in case that the number of OFDM symbols within a DwPTS isgreater than or equal to a specific number (e.g., 11) in Case #2 of Sol3 method, E-PDCCH region may be configured with more than L (e.g., 4)number of OFDM symbols in first and second slots. In this case, it ispossible to directly apply a PDCCH transmission structure and a SSconfiguration to a S SF, which are applied to a general D such as Alt 1or Alt 2 and the like.

Table 6 indicates an example that Sol 3 is applied to Table 5. A shadowindicates the case that Case #1 is applied to a S SF (i.e., except anE-PDCCH reception).

TABLE 6

FIG. 15 illustrates an example of transmitting/receiving a PDCCHaccording to Sol 3. X corresponds to D or U and is given according to aUL-DL configuration. Referring to FIG. 15, E-PDCCHtransmission/detection may be selectively performed according to theUL-DL configuration in a S SF ({circle around (1)}). For instance, if aUL-DL configuration corresponds to the shadows of Table 6 (i.e., Case#1), a PDCCH transmission/detection process may be performed on theassumption that there is no E-PDCCH transmission in a S SF. As oneexample, an E-PDCCH detection process may be omitted or skipped in the SSF. On the other hand, in case that a UL-DL configuration does notcorrespond to the shadows of Table 6 (i.e., case #2), a E-PDCCHtransmission/detection process may be normally performed in a S SF.

Meanwhile, in order to avoid a mutual interference between a LTE TDDsystem deployed in an adjacent frequency and another TDD system (e.g.,time division synchronous code division multiple access (TD-SCDMA)) andin order for the systems to stably coexist, employing a new S SFconfiguration (hereinafter, new-S) is under consideration. Specifically,employing a S configuration in which DwPTS is configured with 6 OFDMsymbols in case of DL normal CP (hereinafter new-S for n-CP) and a Sconfiguration that DwPTS is configured with 5 OFDM symbols in case of DLextended CP (hereinafter, new-S for e-CP) is under consideration.

Table 7 shows an example that a new-S for n-CP and a new-S for e-CP areadded to the conventional S SF configuration (i.e., Table 5). Shadowsindicate the new-S for n-CP and the new-S for e-CP. In case that thenew-S for n-CP and the new-S for e-CP are configured, the length ofUpPTS may be newly defined or may follow the conventional configurationsas exemplarily shown in Table 7.

TABLE 7

In consideration of DwPTS configurations according to the new-S for n-CPand the new-S for e-CP, a transmission mode and a corresponding RSstructure may be applied as follows.

-   -   In case of TM 8 or TM 9        -   for new-S for n-CP, supported is demodulation based on DRMS            (demodulation reference signal) which is transmitted using            antenna ports #7 to #10 via the 3^(rd) and 4^(th) OFDM            symbols (of DwPTS) within the 1^(st) slot.        -   for new-S for e-CP, DMRS-based demodulation is not            supported.    -   In case of TM 7        -   for the new-S for e-CP, supported is demodulation based on            DRMS (demodulation reference signal) which is transmitted            using an antenna port #5 via the 5^(th) OFDM symbol (of            DwPTS) within the 1^(st) slot.        -   for the new-S for n-CP, DMRS-based demodulation is not            supported.

In case of E-PDCCH, in order to enhance transmission performance ofcontrol channels through a UE-specific precoding, DMRS-basedtransmission using antenna ports #7 to #14 or a subset thereof (based onTM 9) may be mainly considered. In this case, since the DMRS-baseddemodulation (of DL data) using antenna ports #7 to #14 or a subsetthereof is not supported, E-PDCCH transmission may be not permitted aswell.

Therefore, although a TDD system is configured to use E-PDCCH, if a S SFis not permitted to use the DMRS-based demodulation using antenna ports#7 to #14 or a subset thereof, the present invention proposes to applySol 2 (i.e., permits/assumes L-PDCCH transmission only) to a S SF. Forinstance, in case that DwPTS is configured with a S configurationconfigured with the specific number (e.g., 3) of OFDM symbols and thenew-S for e-CP, only Sol 2 may be applied (to S SF) (i.e., only L-PDCCHtransmission may be permitted/assumed).

Table 8 shows an example that Sol 3 and the aforementioned additionalproposal are applied to Table 7. Shadows indicate the cases that Case #1is applied to S SF (i.e., except E-PDCCH reception).

TABLE 8

FIG. 16 is a diagram for explaining an example of a base station, arelay, and a user equipment applicable to the present invention.

Referring to FIG. 16, a wireless communication system may include a basestation (BS) 110 and a user equipment (UE) 120. In case that thewireless communication system includes a relay, the base station or theuser equipment may be replaced by the relay.

The base station 110 includes a processor 112, a memory 114 and a radiofrequency (RF) unit 116. The processor 112 may be configured toimplement the procedure and/or methods proposed by the presentinvention. The memory 114 is connected to the processor 112 andconfigured to store various information related to the operation of theprocessor 112. The RF unit 116 is connected to the processor 112 andconfigured to transmit and/or receive a radio signal. The user equipment120 includes a processor 122, a memory 124 and a radio frequency (RF)unit 126. The processor 122 can be configured to implement the procedureand/or methods proposed by the present invention. The memory 124 isconnected to the processor 122 and configured to store variousinformation related to the operation of the processor 122. The RF unit126 is connected to the processor 122 and configured to transmit and/orreceive a radio signal.

The above-mentioned embodiments correspond to combinations of elementsand features of the present invention in prescribed forms. And, it isable to consider that the respective elements or features are selectiveunless they are explicitly mentioned. Each of the elements or featurescan be implemented in a form failing to be combined with other elementsor features. Moreover, it is able to implement an embodiment of thepresent invention by combining elements and/or features together inpart. A sequence of operations explained for each embodiment of thepresent invention can be modified. Some configurations or features ofone embodiment can be included in another embodiment or can besubstituted for corresponding configurations or features of anotherembodiment. And, it is apparently understandable that an embodiment isconfigured by combining claims failing to have relation of explicitcitation in the appended claims together or can be included as newclaims by amendment after filing an application.

In this specification, embodiments of the present invention aredescribed centering on the signal transmission/reception relationsbetween a relay and a base station. The signal transmission/receptionrelation identically/similarly expands to the signaltransmission/reception relation between a user equipment and a basestation or between a user equipment and a relay. In this disclosure, aspecific operation explained as performed by a base station can beoccasionally performed by an upper node of the base station. Inparticular, in a network constructed with a plurality of network nodesincluding a base station, it is apparent that various operationsperformed for communication with a user equipment can be performed by abase station or other networks except the base station. In this case,‘base station’ may be replaced by such a terminology as a fixed station,a Node B, an eNode B (eNB), an access point, and the like. And, ‘userequipment (UE)’ may be replaced by such a terminology as a terminal, amobile station (MS), a mobile subscriber station (MSS) and the like.

Embodiments of the present invention can be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof. In case of the implementation by hardware, a method accordingto each embodiment of the present invention can be implemented by atleast one selected from the group consisting of ASICs (applicationspecific integrated circuits), DSPs (digital signal processors), DSPDs(digital signal processing devices), PLDs (programmable logic devices),FPGAs (field programmable gate arrays), processor, controller,microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in amemory unit and is then drivable by a processor. The memory unit isprovided within or outside the processor to exchange data with theprocessor through the means well-known to the public.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents. And, it isapparently understandable that an embodiment is configured by combiningclaims failing to have relation of explicit citation in the appendedclaims together or can be included as new claims by amendment afterfiling an application.

INDUSTRIAL APPLICABILITY

Accordingly, the present invention can be used by a user equipmentdevice, a base station, or a different device of a wireless mobilecommunication system. Specifically, the present invention can be appliedto a method of transmitting a UL control information and apparatustherefor.

What is claimed is:
 1. A method of receiving a downlink control signalby a user equipment in a TDD (Time Division Duplex)-based wirelesscommunication system, the method comprising: receiving a downlink signalvia a downlink period in a specific subframe comprising the downlinkperiod, a guard period, and an uplink period, wherein a combination ofthe downlink period, the guard period, and the uplink period is given byusing configuration information for the specific subframe, wherein ifthe configuration information is given such that that a length of thedownlink period is greater than a specific value, a detection processfor a PDCCH (physical downlink control channel) of a first type isperformed in the specific subframe, wherein if the configurationinformation is given such that the length of the downlink period isequal to or less than the specific value, the detection process for thePDCCH of the first type is skipped, wherein the PDCCH of the first typeindicates a PDCCH configured within a resource region starting from anN^(th) OFDM symbol in a subframe, and wherein N is an integer of 2 ormore.
 2. The method of claim 1, wherein an extended CP (Cyclic Prefix)is configured for a downlink transmission, and the specific value is 6OFDM symbols.
 3. The method of claim 1, wherein an extended CP isconfigured for a downlink transmission, and the length of the downlinkperiod is given by a following table according to the configurationinformation: Configuration Length of downlink period information (thenumber of OFDM symbols) 0 3 1 8 2 9 3 10 4 3 5 8 6 9 7 5

wherein if the configuration information corresponds to #1, #2, #3, #5or #6, the detection process for the PDCCH of the first type isperformed in the specific subframe, and wherein if the configurationinformation corresponds to #0, #4 or #7, the detection process for thePDCCH of the first type is skipped in the specific subframe.
 4. Themethod of claim 1, wherein a normal CP (cyclic prefix) is configured fora downlink transmission, and the specific value is 3 OFDM symbols. 5.The method of claim 1, a normal CP (cyclic prefix) is configured for adownlink transmission, and the length of the downlink period is given bya following table according to the configuration information:Configuration Length of downlink period information (the number of OFDMsymbols) 0 3 1 9 2 10 3 11 4 12 5 3 6 9 7 10 8 11 9 6

wherein if the configuration information corresponds to #1 to #4 or #6to #9, the detection process for the PDCCH of the first type isperformed in the specific subframe, and wherein if the configurationinformation corresponds to #0 or #5, the detection process for the PDCCHof the first type is skipped in the specific subframe.
 6. The method ofclaim 1, wherein if the configuration information is given such that thelength of the downlink period is equal to or less than the specificvalue, the detection process for a PDCCH of a second type is performedin the specific subframe, and wherein the PDCCH of the second typeindicates a PDCCH configured within a resource region of 0^(th) toN−1^(th) OFDM symbols in a subframe.
 7. A communication device used forin a TDD (Time Division Duplex)-based wireless communication system, thecommunication device comprising: a radio frequency (RF) unit; and aprocessor, wherein the processor is configured to receive a downlinksignal via a downlink period in a specific subframe comprising thedownlink period, a guard period, and an uplink period, wherein acombination of the downlink period, the guard period, and the uplinkperiod is given by using configuration information for the specificsubframe, wherein if the configuration information is given such that alength of the downlink period is greater than a specific value, adetection process for a PDCCH (physical downlink control channel) of afirst type is performed in the specific subframe, wherein if theconfiguration information is given such that the length of the downlinkperiod is equal to or less than the specific value, the detectionprocess for the PDCCH of the first type is skipped, wherein the PDCCH ofthe first type indicates a PDCCH configured within a resource regionstarting from an N^(th) OFDM symbol in a subframe, and wherein N is aninteger of 2 or more.
 8. The communication device of claim 7, wherein anextended CP (Cyclic Prefix) is configured for a downlink transmission,and the specific value is 6 OFDM symbols.
 9. The communication device ofclaim 7, wherein an extended CP is configured for a downlinktransmission, and the length of the downlink period is given by afollowing table according to the configuration information:Configuration Length of downlink period information (the number of OFDMsymbols) 0 3 1 8 2 9 3 10 4 3 5 8 6 9 7 5

wherein if the configuration information corresponds to #1, #2, #3, #5or #6, the detection process for the PDCCH of the first type isperformed in the specific subframe, and wherein if the configurationinformation corresponds to #0, #4 or #7, the detection process for thePDCCH of the first type is skipped in the specific subframe.
 10. Thecommunication device of claim 7, wherein a normal CP (cyclic prefix) isconfigured for a downlink transmission, and the specific value is 3 OFDMsymbols.
 11. The communication device of claim 7, a normal CP (cyclicprefix) is configured for a downlink transmission, and the length of thedownlink period is given by a following table according to theconfiguration information: Configuration Length of downlink periodinformation (the number of OFDM symbols) 0 3 1 9 2 10 3 11 4 12 5 3 6 97 10 8 11 9 6

wherein if the configuration information corresponds to #1 to #4 or #6to #9, the detection process for the PDCCH of the first type isperformed in the specific subframe, and wherein if the configurationinformation corresponds to #0 or #5, the detection process for the PDCCHof the first type is skipped in the specific subframe.
 12. Thecommunication device of claim 7, wherein if the configurationinformation is given such that that the length of the downlink period isequal to or less than the specific value, the detection process for aPDCCH of a second type is performed in the specific subframe and whereinthe PDCCH of the second type indicates a PDCCH configured within aresource region of 0^(th) to N−1^(th) OFDM symbols in a subframe.